Strain Improvement in Tylosin Producing Streptomyces fradiae by Mutagenesis

Streptomyces fradiae NRRL 2702 was mutagenized using N-methyl-N-nitro-N-nitrosoguanidine (MNNG) and ultraviolet (UV) to improve tylosin yield. An increase of 86.47% was observed when colonies of S. fradiae were exposed to MNNG. Out of 144 colonies, mutant No. 93 was the highest tylosin producer as shown by their inhibition of Micrococcus luteus growth. Further strain improvement of this mutant was done using UV and MNNG-UV double mutagenesis. Out of 473 isolates screened, 34 isolates (28 UV treated) manifested higher yield. However, only three isolates (two MNNG treated and one MNNG-UV treated) were found to have significantly higher yields than the parent strain. An increase of 69% tylosin yield was observed with NA-3 mutant using MNNG-UV mutagenesis. However, most of the improved strains were not stable and only the MNNG treated strain No. 93 remained stable even after three years. Key words: Streptomyces fradiae , mutagenesis, tylosin